
<!DOCTYPE HTML>
<html lang="zh-hans" >
<head>
    <meta charset="UTF-8">
    <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
    <title>14.2：Element和BuildContext · 《Flutter实战》</title>
    <meta http-equiv="X-UA-Compatible" content="IE=edge"/>
    <meta name="baidu-site-verification" content="Y34sAqDKUH"/>
    <meta name="theme-color" content="#ffffff">
    <!--<meta name="description" content="">-->
    <meta name="description" content="《Flutter实战》是Flutter中文网（https://flutterchina.club）开源的电子书，旨在帮助开发者系统化的了解并学习Flutter。">
    <meta name="keywords" content="flutter实战,flutter书籍,flutter电子书,flutter中文网 ">
    <meta name="generator" content="GitBook 3.2.3">
    
    <meta name="author" content="wendux 824783146@qq.com">
    
    
    
    
    <link rel="stylesheet" href="https://pcdn.flutterchina.club/gitbook/style.css">

    
    
    
    <link rel="stylesheet" href="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-search-pro/search.css">
    
    
    
    <link rel="stylesheet" href="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-ace/ace.css">
    
    
    
    <link rel="stylesheet" href="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-splitter/splitter.css">
    
    
    
    <link rel="stylesheet" href="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-prism/prism.css">
    
    
    
    <link rel="stylesheet" href="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-donate/plugin.css">
    
    
    
    <link rel="stylesheet" href="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-fontsettings/website.css">
    
    
    

    

    
        
    
        
    
        
    
        
    
        
    

    
    
    
    <meta name="HandheldFriendly" content="true"/>
    <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black">
    <link rel="apple-touch-icon-precomposed" sizes="152x152" href="https://pcdn.flutterchina.club/gitbook/images/apple-touch-icon-precomposed-152.png">
    <link rel="shortcut icon" href="https://pcdn.flutterchina.club/gitbook/images/favicon.ico" type="image/x-icon">

    
    <link rel="next" href="render_object.html" />
    
    
    <link rel="prev" href="flutter_ui_system.html" />
    

    <style>
        .pull-right > i {
            font-size: 25px;
            color: #777 !important;
            cursor: pointer;

        }

        .pull-right > i:hover {
            color: #777 !important;
        }

        body {
            font-size: 15px !important;
        }

        a[href='../todo.html'], a[href='todo.html'] {
            color: #888 !important;
        }

        .copyright {
            text-align: center;
            margin: 80px 16px 8px 16px;
            padding-top: 16px;
            border-top: #eee 1px solid;
            color: grey;
            font-size: .9em;
        }

        .f-links a{
            text-decoration: underline;
            color: dodgerblue !important;
        }

        .f-links a:hover{
            opacity: .8 !important;
        }

        /*.ad {*/
            /*color: white;*/
            /*text-align: center;*/
            /*background: url(https://img.alicdn.com/tfs/TB1Huu7vMmTBuNjy1XbXXaMrVXa-2880-400.png);*/
            /*background-size: cover;*/
            /*cursor: pointer;*/
            /*margin-bottom: 30px;*/
            /*padding: 18px*/
        /*}*/

        /*.ad:hover {*/
            /*opacity: .8;*/
        /*}*/

        .buy-btn {
            text-decoration: none !important;
            padding: 8px 18px;
            border: #268bd2 1px solid !important;
            display: inline-block !important;
            border-radius: 25px;
            color: #268bd2;
            margin-top: 10px;
        }

        .buy-btn:hover {
            transition: all ease 200ms;
            box-shadow: #555 2px 5px 10px;
            background: #eee;
            color: dodgerblue !important;
        }

        .maoyun{
            padding-top: 5px;
        }


    </style>
</head>
<body>
<!--<div id="ad" style="display: none">-->
<!--<div class="ad ad0"-->
<!--onclick="_track('aliyun','https://promotion.aliyun.com/ntms/yunparter/invite.html?userCode=8hhi4dts')">-->
<!--<div style="font-size: 1.3em; padding-right: 120px; position: relative; top: 12px">阿里云新春特惠</div>-->
<!--<div style="color:orange; font-size: 13px">限时红包 最高￥<span style="font-size: 40px">1888</span></div>-->
<!--</div>-->
<!--<div class="ad ad1"-->
<!--onclick="_track('aliyun-puhui','https://promotion.aliyun.com/ntms/act/qwbk.html?spm=5176.11533457.1089570.10.74e877e33jtaGy&userCode=8hhi4dts')">-->
<!--<div style="font-size: 1.5em;">阿里云全民云计算-新春特惠</div>-->
<!--<div style="color:orange; font-size: 18px;padding-top: 4px;">普惠上云，云服务器1核1G仅需293元/年</div>-->
<!--</div>-->
<!--</div>-->

<div class="ad"  style="text-align:center; padding-bottom:30px; display: none"><a href="https://item.jd.com/12816296.html" onclick="buy('img')" title='点击购买' target="_blank"><img style="height:250px;box-shadow: #aaa 5px 5px 10px;" src="https://pcdn.flutterchina.club/imgs/book.png"/></a>  <br/> <a class="buy-btn" onclick="buy('img')" href="https://item.jd.com/12816296.html" title='点击购买' target="_blank"> 购买实体书 </a></div>


<div class="book">
    <div class="book-summary">
        
            
<div id="book-search-input" role="search">
    <input type="text" placeholder="输入并搜索" />
</div>

            
                <nav role="navigation">
                


<ul class="summary">
    
    
    
        
        <li>
            <a href="https://flutterchina.club" target="_blank" class="custom-link"><div><img height=20 style='position:relative; top:5px; padding-right:5px ' src='https://cdn.jsdelivr.net/gh/flutterchina/website@1.0/images/favicon.png'/> Flutter中文网</div></a>
        </li>
    
    

    
    <li class="divider"></li>
    

    
        
        
    
        <li class="chapter " data-level="1.1" data-path="../">
            
                <a href="../">
            
                    
                    简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="1.2" data-path="../intro.html">
            
                <a href="../intro.html">
            
                    
                    前言
            
                </a>
            

            
        </li>
    

    
        
        <li class="header">入门篇</li>
        
        
    
        <li class="chapter " data-level="2.1" data-path="../chapter1/">
            
                <a href="../chapter1/">
            
                    
                    第一章：起步
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.1.1" data-path="../chapter1/mobile_development_intro.html">
            
                <a href="../chapter1/mobile_development_intro.html">
            
                    
                    1.1：移动开发技术简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.1.2" data-path="../chapter1/flutter_intro.html">
            
                <a href="../chapter1/flutter_intro.html">
            
                    
                    1.2：初识Flutter
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.1.3" data-path="../chapter1/install_flutter.html">
            
                <a href="../chapter1/install_flutter.html">
            
                    
                    1.3：搭建Flutter开发环境
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.1.4" data-path="../chapter1/dart.html">
            
                <a href="../chapter1/dart.html">
            
                    
                    1.4：Dart语言简介
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="2.2" data-path="../chapter2/">
            
                <a href="../chapter2/">
            
                    
                    第二章：第一个Flutter应用
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.2.1" data-path="../chapter2/first_flutter_app.html">
            
                <a href="../chapter2/first_flutter_app.html">
            
                    
                    2.1：计数器示例
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.2.2" data-path="../chapter2/flutter_router.html">
            
                <a href="../chapter2/flutter_router.html">
            
                    
                    2.2：路由管理
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.2.3" data-path="../chapter2/flutter_package_mgr.html">
            
                <a href="../chapter2/flutter_package_mgr.html">
            
                    
                    2.3：包管理
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.2.4" data-path="../chapter2/flutter_assets_mgr.html">
            
                <a href="../chapter2/flutter_assets_mgr.html">
            
                    
                    2.4：资源管理
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.2.5" data-path="../chapter2/flutter_app_debug.html">
            
                <a href="../chapter2/flutter_app_debug.html">
            
                    
                    2.5：调试Flutter APP
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.2.6" data-path="../chapter2/thread_model_and_error_report.html">
            
                <a href="../chapter2/thread_model_and_error_report.html">
            
                    
                    2.6：Dart线程模型及异常捕获
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="2.3" data-path="../chapter3/">
            
                <a href="../chapter3/">
            
                    
                    第三章：基础组件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.3.1" data-path="../chapter3/flutter_widget_intro.html">
            
                <a href="../chapter3/flutter_widget_intro.html">
            
                    
                    3.1：Widget简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.3.2" data-path="../chapter3/state_manage.html">
            
                <a href="../chapter3/state_manage.html">
            
                    
                    3.2：状态管理
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.3.3" data-path="../chapter3/text.html">
            
                <a href="../chapter3/text.html">
            
                    
                    3.3：文本、字体样式
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.3.4" data-path="../chapter3/buttons.html">
            
                <a href="../chapter3/buttons.html">
            
                    
                    3.4：按钮
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.3.5" data-path="../chapter3/img_and_icon.html">
            
                <a href="../chapter3/img_and_icon.html">
            
                    
                    3.5：图片和Icon
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.3.6" data-path="../chapter3/radio_and_checkbox.html">
            
                <a href="../chapter3/radio_and_checkbox.html">
            
                    
                    3.6：单选框和复选框
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.3.7" data-path="../chapter3/input_and_form.html">
            
                <a href="../chapter3/input_and_form.html">
            
                    
                    3.7：输入框和表单
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.3.8" data-path="../chapter3/progress.html">
            
                <a href="../chapter3/progress.html">
            
                    
                    3.8：进度指示器
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="2.4" data-path="../chapter4/">
            
                <a href="../chapter4/">
            
                    
                    第四章：布局类组件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.4.1" data-path="../chapter4/intro.html">
            
                <a href="../chapter4/intro.html">
            
                    
                    4.1：布局类组件简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.4.2" data-path="../chapter4/row_and_column.html">
            
                <a href="../chapter4/row_and_column.html">
            
                    
                    4.2：线性布局（Row、Column）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.4.3" data-path="../chapter4/flex.html">
            
                <a href="../chapter4/flex.html">
            
                    
                    4.3：弹性布局（Flex）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.4.4" data-path="../chapter4/wrap_and_flow.html">
            
                <a href="../chapter4/wrap_and_flow.html">
            
                    
                    4.4：流式布局（Wrap、Flow）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.4.5" data-path="../chapter4/stack.html">
            
                <a href="../chapter4/stack.html">
            
                    
                    4.5：层叠布局（Stack、Positioned）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.4.6" data-path="../chapter4/alignment.html">
            
                <a href="../chapter4/alignment.html">
            
                    
                    4.6：对齐与相对定位（Align）
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="2.5" data-path="../chapter5/">
            
                <a href="../chapter5/">
            
                    
                    第五章：容器类组件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.5.1" data-path="../chapter5/padding.html">
            
                <a href="../chapter5/padding.html">
            
                    
                    5.1：填充（Padding）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.5.2" data-path="../chapter5/constrainedbox_and_sizebox.html">
            
                <a href="../chapter5/constrainedbox_and_sizebox.html">
            
                    
                    5.2：尺寸限制类容器（ConstrainedBox等）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.5.3" data-path="../chapter5/decoratedbox.html">
            
                <a href="../chapter5/decoratedbox.html">
            
                    
                    5.3：装饰容器（DecoratedBox）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.5.4" data-path="../chapter5/transform.html">
            
                <a href="../chapter5/transform.html">
            
                    
                    5.4：变换（Transform）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.5.5" data-path="../chapter5/container.html">
            
                <a href="../chapter5/container.html">
            
                    
                    5.5：Container容器
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.5.6" data-path="../chapter5/material_scaffold.html">
            
                <a href="../chapter5/material_scaffold.html">
            
                    
                    5.6：Scaffold、TabBar、底部导航
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.5.7" data-path="../chapter5/clip.html">
            
                <a href="../chapter5/clip.html">
            
                    
                    5.7：剪裁（Clip）
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="2.6" data-path="../chapter6/">
            
                <a href="../chapter6/">
            
                    
                    第六章：可滚动组件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.6.1" data-path="../chapter6/intro.html">
            
                <a href="../chapter6/intro.html">
            
                    
                    6.1：可滚动组件简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.6.2" data-path="../chapter6/single_child_scrollview.html">
            
                <a href="../chapter6/single_child_scrollview.html">
            
                    
                    6.2：SingleChildScrollView
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.6.3" data-path="../chapter6/listview.html">
            
                <a href="../chapter6/listview.html">
            
                    
                    6.3：ListView
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.6.4" data-path="../chapter6/gridview.html">
            
                <a href="../chapter6/gridview.html">
            
                    
                    6.4：GridView
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.6.5" data-path="../chapter6/custom_scrollview.html">
            
                <a href="../chapter6/custom_scrollview.html">
            
                    
                    6.5：CustomScrollView
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.6.6" data-path="../chapter6/scroll_controller.html">
            
                <a href="../chapter6/scroll_controller.html">
            
                    
                    6.6：滚动监听及控制（ScrollController）
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="2.7" data-path="../chapter7/">
            
                <a href="../chapter7/">
            
                    
                    第七章：功能型组件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="2.7.1" data-path="../chapter7/willpopscope.html">
            
                <a href="../chapter7/willpopscope.html">
            
                    
                    7.1：导航返回拦截（WillPopScope）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.7.2" data-path="../chapter7/inherited_widget.html">
            
                <a href="../chapter7/inherited_widget.html">
            
                    
                    7.2：数据共享（InheritedWidget）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.7.3" data-path="../chapter7/provider.html">
            
                <a href="../chapter7/provider.html">
            
                    
                    7.3： 跨组件状态共享（Provider）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.7.4" data-path="../chapter7/theme.html">
            
                <a href="../chapter7/theme.html">
            
                    
                    7.4：颜色和主题（Theme）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.7.5" data-path="../chapter7/futurebuilder_and_streambuilder.html">
            
                <a href="../chapter7/futurebuilder_and_streambuilder.html">
            
                    
                    7.5：异步UI更新（FutureBuilder、StreamBuilder）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="2.7.6" data-path="../chapter7/dailog.html">
            
                <a href="../chapter7/dailog.html">
            
                    
                    7.6：对话框详解
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    

    
        
        <li class="header">进阶篇</li>
        
        
    
        <li class="chapter " data-level="3.1" data-path="../chapter8/">
            
                <a href="../chapter8/">
            
                    
                    第八章：事件处理与通知
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.1.1" data-path="../chapter8/listener.html">
            
                <a href="../chapter8/listener.html">
            
                    
                    8.1：原始指针事件处理
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.1.2" data-path="../chapter8/gesture.html">
            
                <a href="../chapter8/gesture.html">
            
                    
                    8.2：手势识别
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.1.3" data-path="../chapter8/eventbus.html">
            
                <a href="../chapter8/eventbus.html">
            
                    
                    8.3：全局事件总线
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.1.4" data-path="../chapter8/notification.html">
            
                <a href="../chapter8/notification.html">
            
                    
                    8.4：通知(Notification)
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.2" data-path="../chapter9/">
            
                <a href="../chapter9/">
            
                    
                    第九章：动画
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.2.1" data-path="../chapter9/intro.html">
            
                <a href="../chapter9/intro.html">
            
                    
                    9.1：Flutter动画简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.2.2" data-path="../chapter9/animation_structure.html">
            
                <a href="../chapter9/animation_structure.html">
            
                    
                    9.2：动画结构
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.2.3" data-path="../chapter9/route_transition.html">
            
                <a href="../chapter9/route_transition.html">
            
                    
                    9.3：自定义路由过渡动画
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.2.4" data-path="../chapter9/hero.html">
            
                <a href="../chapter9/hero.html">
            
                    
                    9.4：Hero动画
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.2.5" data-path="../chapter9/stagger_animation.html">
            
                <a href="../chapter9/stagger_animation.html">
            
                    
                    9.5：交织动画
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.2.6" data-path="../chapter9/animated_switcher.html">
            
                <a href="../chapter9/animated_switcher.html">
            
                    
                    9.6：通用“动画切换”组件（AnimatedSwitcher）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.2.7" data-path="../chapter9/animated_widgets.html">
            
                <a href="../chapter9/animated_widgets.html">
            
                    
                    9.7：动画过渡组件
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.3" data-path="../chapter10/">
            
                <a href="../chapter10/">
            
                    
                    第十章：自定义组件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.3.1" data-path="../chapter10/intro.html">
            
                <a href="../chapter10/intro.html">
            
                    
                    10.1：自定义组件方法简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.2" data-path="../chapter10/combine.html">
            
                <a href="../chapter10/combine.html">
            
                    
                    10.2：组合现有组件
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.3" data-path="../chapter10/turn_box.html">
            
                <a href="../chapter10/turn_box.html">
            
                    
                    10.3：组合实例：TurnBox
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.4" data-path="../chapter10/custom_paint.html">
            
                <a href="../chapter10/custom_paint.html">
            
                    
                    10.4：自绘组件（CustomPaint与Canvas）
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.3.5" data-path="../chapter10/gradient_circular_progress_demo.html">
            
                <a href="../chapter10/gradient_circular_progress_demo.html">
            
                    
                    10.5：自绘实例：圆形渐变进度条(自绘)
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.4" data-path="../chapter11/">
            
                <a href="../chapter11/">
            
                    
                    第十一章：文件操作与网络请求
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.4.1" data-path="../chapter11/file_operation.html">
            
                <a href="../chapter11/file_operation.html">
            
                    
                    11.1：文件操作
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.2" data-path="../chapter11/http.html">
            
                <a href="../chapter11/http.html">
            
                    
                    11.2：Http请求-HttpClient
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.3" data-path="../chapter11/dio.html">
            
                <a href="../chapter11/dio.html">
            
                    
                    11.3：Http请求-Dio package
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.4" data-path="../chapter11/download_with_chunks.html">
            
                <a href="../chapter11/download_with_chunks.html">
            
                    
                    11.4：实例：Http分块下载
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.5" data-path="../chapter11/websocket.html">
            
                <a href="../chapter11/websocket.html">
            
                    
                    11.5：WebSocket
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.6" data-path="../chapter11/socket.html">
            
                <a href="../chapter11/socket.html">
            
                    
                    11.6：使用Socket API
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.4.7" data-path="../chapter11/json_model.html">
            
                <a href="../chapter11/json_model.html">
            
                    
                    11.7：Json转Dart Model类
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.5" data-path="../chapter12/">
            
                <a href="../chapter12/">
            
                    
                    第十二章：包与插件
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.5.1" data-path="../chapter12/develop_package.html">
            
                <a href="../chapter12/develop_package.html">
            
                    
                    12.1：开发package
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.2" data-path="../chapter12/platform-channel.html">
            
                <a href="../chapter12/platform-channel.html">
            
                    
                    12.2：平台通道简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.3" data-path="../chapter12/develop_plugin.html">
            
                <a href="../chapter12/develop_plugin.html">
            
                    
                    12.3：开发Flutter插件
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.4" data-path="../chapter12/android_implement.html">
            
                <a href="../chapter12/android_implement.html">
            
                    
                    12.4：插件开发：实现Android端API
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.5" data-path="../chapter12/ios_implement.html">
            
                <a href="../chapter12/ios_implement.html">
            
                    
                    12.5：插件开发：实现IOS端API
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.5.6" data-path="../chapter12/texture_platformview.html">
            
                <a href="../chapter12/texture_platformview.html">
            
                    
                    12.6：Texture和PlatformView
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.6" data-path="../chapter13/">
            
                <a href="../chapter13/">
            
                    
                    第十三章：国际化
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.6.1" data-path="../chapter13/multi_languages_support.html">
            
                <a href="../chapter13/multi_languages_support.html">
            
                    
                    13.1：让App支持多语言
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.6.2" data-path="../chapter13/locallization_implement.html">
            
                <a href="../chapter13/locallization_implement.html">
            
                    
                    13.2：实现Localizations
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.6.3" data-path="../chapter13/intl.html">
            
                <a href="../chapter13/intl.html">
            
                    
                    13.3：使用Intl包
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.6.4" data-path="../chapter13/faq.html">
            
                <a href="../chapter13/faq.html">
            
                    
                    13.4：国际化常见问题
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    
        <li class="chapter " data-level="3.7" data-path="./">
            
                <a href="./">
            
                    
                    第十四章：Flutter核心原理
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="3.7.1" data-path="flutter_ui_system.html">
            
                <a href="flutter_ui_system.html">
            
                    
                    14.1：Flutter UI系统
            
                </a>
            

            
        </li>
    
        <li class="chapter active" data-level="3.7.2" data-path="element_buildcontext.html">
            
                <a href="element_buildcontext.html">
            
                    
                    14.2：Element和BuildContext
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.7.3" data-path="render_object.html">
            
                <a href="render_object.html">
            
                    
                    14.3：RenderObject与RenderBox
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.7.4" data-path="flutter_app_startup.html">
            
                <a href="flutter_app_startup.html">
            
                    
                    14.4：Flutter从启动到显示
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="3.7.5" data-path="image_and_cache.html">
            
                <a href="image_and_cache.html">
            
                    
                    14.5：Flutter图片加载与缓存
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    

    
        
        <li class="header">实例篇</li>
        
        
    
        <li class="chapter " data-level="4.1" data-path="../chapter15/intro.html">
            
                <a href="../chapter15/intro.html">
            
                    
                    第十五章：一个完整的Flutter应用
            
                </a>
            

            
            <ul class="articles">
                
    
        <li class="chapter " data-level="4.1.1" data-path="../chapter15/intro.html">
            
                <a href="../chapter15/intro.html">
            
                    
                    15.1：应用简介
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.2" data-path="../chapter15/code_structure.html">
            
                <a href="../chapter15/code_structure.html">
            
                    
                    15.2：APP代码结构
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.3" data-path="../chapter15/models.html">
            
                <a href="../chapter15/models.html">
            
                    
                    15.3：Model类定义
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.4" data-path="../chapter15/globals.html">
            
                <a href="../chapter15/globals.html">
            
                    
                    15.4：全局变量及共享状态
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.5" data-path="../chapter15/network.html">
            
                <a href="../chapter15/network.html">
            
                    
                    15.5：网络请求封装
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.6" data-path="../chapter15/entry.html">
            
                <a href="../chapter15/entry.html">
            
                    
                    15.6：App入口及首页
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.7" data-path="../chapter15/login_page.html">
            
                <a href="../chapter15/login_page.html">
            
                    
                    15.7：登录页
            
                </a>
            

            
        </li>
    
        <li class="chapter " data-level="4.1.8" data-path="../chapter15/language_and_theme_setting.html">
            
                <a href="../chapter15/language_and_theme_setting.html">
            
                    
                    15.8：多语言和多主题
            
                </a>
            

            
        </li>
    

            </ul>
            
        </li>
    

    

    <li class="divider"></li>

    <li>
        <a href="https://www.gitbook.com" target="blank" class="https://pcdn.flutterchina.club/gitbook-link">
            本书使用 GitBook 发布
        </a>
    </li>
</ul>


                </nav>
            
        
    </div>

    <div class="book-body">
        
            <div class="body-inner">
                
                    

<div class="book-header" role="navigation">
    
    <a class="btn pull-right" aria-label="GitHub">
        <i class="fa fa-edit" title="编辑本文"></i>
    </a>
    <a class="btn pull-right" aria-label="GitHub" href="https://github.com/flutterchina/flutter-in-action">
        <i class="fa fa-github" title="查看本书开源项目"></i>
    </a>
    <!-- Title -->
    <h1>
        <i class="fa fa-circle-o-notch fa-spin"></i>
        <a href=".." >14.2：Element和BuildContext</a>
    </h1>
</div>




                    <div class="page-wrapper" tabindex="-1" role="main">
                        <div class="page-inner">
                            
<div id="book-search-results">
    <div class="search-noresults">
    
                                <section class="normal markdown-section">
                                
                                <h1 id="142-element&#x4E0E;buildcontext">14.2 Element&#x4E0E;BuildContext</h1>
<h2 id="1421-element">14.2.1 Element</h2>
<p>&#x5728;&#x201C;Widget&#x7B80;&#x4ECB;&#x201D;&#x4E00;&#x8282;&#xFF0C;&#x6211;&#x4EEC;&#x4ECB;&#x7ECD;&#x4E86;Widget&#x548C;Element&#x7684;&#x5173;&#x7CFB;&#xFF0C;&#x6211;&#x4EEC;&#x77E5;&#x9053;&#x6700;&#x7EC8;&#x7684;UI&#x6811;&#x5176;&#x5B9E;&#x662F;&#x7531;&#x4E00;&#x4E2A;&#x4E2A;&#x72EC;&#x7ACB;&#x7684;Element&#x8282;&#x70B9;&#x6784;&#x6210;&#x3002;&#x6211;&#x4EEC;&#x4E5F;&#x8BF4;&#x8FC7;&#x7EC4;&#x4EF6;&#x6700;&#x7EC8;&#x7684;Layout&#x3001;&#x6E32;&#x67D3;&#x90FD;&#x662F;&#x901A;&#x8FC7;<code>RenderObject</code>&#x6765;&#x5B8C;&#x6210;&#x7684;&#xFF0C;&#x4ECE;&#x521B;&#x5EFA;&#x5230;&#x6E32;&#x67D3;&#x7684;&#x5927;&#x4F53;&#x6D41;&#x7A0B;&#x662F;&#xFF1A;&#x6839;&#x636E;Widget&#x751F;&#x6210;Element&#xFF0C;&#x7136;&#x540E;&#x521B;&#x5EFA;&#x76F8;&#x5E94;&#x7684;<code>RenderObject</code>&#x5E76;&#x5173;&#x8054;&#x5230;<code>Element.renderObject</code>&#x5C5E;&#x6027;&#x4E0A;&#xFF0C;&#x6700;&#x540E;&#x518D;&#x901A;&#x8FC7;<code>RenderObject</code>&#x6765;&#x5B8C;&#x6210;&#x5E03;&#x5C40;&#x6392;&#x5217;&#x548C;&#x7ED8;&#x5236;&#x3002;</p>
<p>Element&#x5C31;&#x662F;Widget&#x5728;UI&#x6811;&#x5177;&#x4F53;&#x4F4D;&#x7F6E;&#x7684;&#x4E00;&#x4E2A;&#x5B9E;&#x4F8B;&#x5316;&#x5BF9;&#x8C61;&#xFF0C;&#x5927;&#x591A;&#x6570;Element&#x53EA;&#x6709;&#x552F;&#x4E00;&#x7684;<code>renderObject</code>&#xFF0C;&#x4F46;&#x8FD8;&#x6709;&#x4E00;&#x4E9B;Element&#x4F1A;&#x6709;&#x591A;&#x4E2A;&#x5B50;&#x8282;&#x70B9;&#xFF0C;&#x5982;&#x7EE7;&#x627F;&#x81EA;<code>RenderObjectElement</code>&#x7684;&#x4E00;&#x4E9B;&#x7C7B;&#xFF0C;&#x6BD4;&#x5982;<code>MultiChildRenderObjectElement</code>&#x3002;&#x6700;&#x7EC8;&#x6240;&#x6709;Element&#x7684;RenderObject&#x6784;&#x6210;&#x4E00;&#x68F5;&#x6811;&#xFF0C;&#x6211;&#x4EEC;&#x79F0;&#x4E4B;&#x4E3A;&#x201D;Render Tree&#x201C;&#x5373;&#x201D;&#x6E32;&#x67D3;&#x6811;&#x201C;&#x3002;&#x603B;&#x7ED3;&#x4E00;&#x4E0B;&#xFF0C;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x8BA4;&#x4E3A;Flutter&#x7684;UI&#x7CFB;&#x7EDF;&#x5305;&#x542B;&#x4E09;&#x68F5;&#x6811;&#xFF1A;Widget&#x6811;&#x3001;Element&#x6811;&#x3001;&#x6E32;&#x67D3;&#x6811;&#x3002;&#x4ED6;&#x4EEC;&#x7684;&#x4F9D;&#x8D56;&#x5173;&#x7CFB;&#x662F;&#xFF1A;Element&#x6811;&#x6839;&#x636E;Widget&#x6811;&#x751F;&#x6210;&#xFF0C;&#x800C;&#x6E32;&#x67D3;&#x6811;&#x53C8;&#x4F9D;&#x8D56;&#x4E8E;Element&#x6811;&#xFF0C;&#x5982;&#x56FE;14-0&#x6240;&#x793A;&#x3002;</p>
<p><img src="https://pcdn.flutterchina.club/imgs/14-0.png" alt="&#x56FE;14-0"></p>
<p>&#x73B0;&#x5728;&#x6211;&#x4EEC;&#x91CD;&#x70B9;&#x770B;&#x4E00;&#x4E0B;Element&#xFF0C;Element&#x7684;&#x751F;&#x547D;&#x5468;&#x671F;&#x5982;&#x4E0B;&#xFF1A;</p>
<ol>
<li>Framework &#x8C03;&#x7528;<code>Widget.createElement</code> &#x521B;&#x5EFA;&#x4E00;&#x4E2A;Element&#x5B9E;&#x4F8B;&#xFF0C;&#x8BB0;&#x4E3A;<code>element</code></li>
<li>Framework &#x8C03;&#x7528; <code>element.mount(parentElement,newSlot)</code> &#xFF0C;mount&#x65B9;&#x6CD5;&#x4E2D;&#x9996;&#x5148;&#x8C03;&#x7528;<code>element</code>&#x6240;&#x5BF9;&#x5E94;Widget&#x7684;<code>createRenderObject</code>&#x65B9;&#x6CD5;&#x521B;&#x5EFA;&#x4E0E;<code>element</code>&#x76F8;&#x5173;&#x8054;&#x7684;RenderObject&#x5BF9;&#x8C61;&#xFF0C;&#x7136;&#x540E;&#x8C03;&#x7528;<code>element.attachRenderObject</code>&#x65B9;&#x6CD5;&#x5C06;<code>element.renderObject</code>&#x6DFB;&#x52A0;&#x5230;&#x6E32;&#x67D3;&#x6811;&#x4E2D;&#x63D2;&#x69FD;&#x6307;&#x5B9A;&#x7684;&#x4F4D;&#x7F6E;&#xFF08;&#x8FD9;&#x4E00;&#x6B65;&#x4E0D;&#x662F;&#x5FC5;&#x987B;&#x7684;&#xFF0C;&#x4E00;&#x822C;&#x53D1;&#x751F;&#x5728;Element&#x6811;&#x7ED3;&#x6784;&#x53D1;&#x751F;&#x53D8;&#x5316;&#x65F6;&#x624D;&#x9700;&#x8981;&#x91CD;&#x65B0;attach&#xFF09;&#x3002;&#x63D2;&#x5165;&#x5230;&#x6E32;&#x67D3;&#x6811;&#x540E;&#x7684;<code>element</code>&#x5C31;&#x5904;&#x4E8E;&#x201C;active&#x201D;&#x72B6;&#x6001;&#xFF0C;&#x5904;&#x4E8E;&#x201C;active&#x201D;&#x72B6;&#x6001;&#x540E;&#x5C31;&#x53EF;&#x4EE5;&#x663E;&#x793A;&#x5728;&#x5C4F;&#x5E55;&#x4E0A;&#x4E86;&#xFF08;&#x53EF;&#x4EE5;&#x9690;&#x85CF;&#xFF09;&#x3002;</li>
<li>&#x5F53;&#x6709;&#x7236;Widget&#x7684;&#x914D;&#x7F6E;&#x6570;&#x636E;&#x6539;&#x53D8;&#x65F6;&#xFF0C;&#x540C;&#x65F6;&#x5176;<code>State.build</code>&#x8FD4;&#x56DE;&#x7684;Widget&#x7ED3;&#x6784;&#x4E0E;&#x4E4B;&#x524D;&#x4E0D;&#x540C;&#xFF0C;&#x6B64;&#x65F6;&#x5C31;&#x9700;&#x8981;&#x91CD;&#x65B0;&#x6784;&#x5EFA;&#x5BF9;&#x5E94;&#x7684;Element&#x6811;&#x3002;&#x4E3A;&#x4E86;&#x8FDB;&#x884C;Element&#x590D;&#x7528;&#xFF0C;&#x5728;Element&#x91CD;&#x65B0;&#x6784;&#x5EFA;&#x524D;&#x4F1A;&#x5148;&#x5C1D;&#x8BD5;&#x662F;&#x5426;&#x53EF;&#x4EE5;&#x590D;&#x7528;&#x65E7;&#x6811;&#x4E0A;&#x76F8;&#x540C;&#x4F4D;&#x7F6E;&#x7684;element&#xFF0C;element&#x8282;&#x70B9;&#x5728;&#x66F4;&#x65B0;&#x524D;&#x90FD;&#x4F1A;&#x8C03;&#x7528;&#x5176;&#x5BF9;&#x5E94;Widget&#x7684;<code>canUpdate</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5982;&#x679C;&#x8FD4;&#x56DE;<code>true</code>&#xFF0C;&#x5219;&#x590D;&#x7528;&#x65E7;Element&#xFF0C;&#x65E7;&#x7684;Element&#x4F1A;&#x4F7F;&#x7528;&#x65B0;Widget&#x914D;&#x7F6E;&#x6570;&#x636E;&#x66F4;&#x65B0;&#xFF0C;&#x53CD;&#x4E4B;&#x5219;&#x4F1A;&#x521B;&#x5EFA;&#x4E00;&#x4E2A;&#x65B0;&#x7684;Element&#x3002;<code>Widget.canUpdate</code>&#x4E3B;&#x8981;&#x662F;&#x5224;&#x65AD;<code>newWidget</code>&#x4E0E;<code>oldWidget</code>&#x7684;<code>runtimeType</code>&#x548C;<code>key</code>&#x662F;&#x5426;&#x540C;&#x65F6;&#x76F8;&#x7B49;&#xFF0C;&#x5982;&#x679C;&#x540C;&#x65F6;&#x76F8;&#x7B49;&#x5C31;&#x8FD4;&#x56DE;<code>true</code>&#xFF0C;&#x5426;&#x5219;&#x5C31;&#x4F1A;&#x8FD4;&#x56DE;<code>false</code>&#x3002;&#x6839;&#x636E;&#x8FD9;&#x4E2A;&#x539F;&#x7406;&#xFF0C;&#x5F53;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x5F3A;&#x5236;&#x66F4;&#x65B0;&#x4E00;&#x4E2A;Widget&#x65F6;&#xFF0C;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;&#x6307;&#x5B9A;&#x4E0D;&#x540C;&#x7684;Key&#x6765;&#x907F;&#x514D;&#x590D;&#x7528;&#x3002;</li>
<li>&#x5F53;&#x6709;&#x7956;&#x5148;Element&#x51B3;&#x5B9A;&#x8981;&#x79FB;&#x9664;<code>element</code> &#x65F6;&#xFF08;&#x5982;Widget&#x6811;&#x7ED3;&#x6784;&#x53D1;&#x751F;&#x4E86;&#x53D8;&#x5316;&#xFF0C;&#x5BFC;&#x81F4;<code>element</code>&#x5BF9;&#x5E94;&#x7684;Widget&#x88AB;&#x79FB;&#x9664;&#xFF09;&#xFF0C;&#x8FD9;&#x65F6;&#x8BE5;&#x7956;&#x5148;Element&#x5C31;&#x4F1A;&#x8C03;&#x7528;<code>deactivateChild</code> &#x65B9;&#x6CD5;&#x6765;&#x79FB;&#x9664;&#x5B83;&#xFF0C;&#x79FB;&#x9664;&#x540E;<code>element.renderObject</code>&#x4E5F;&#x4F1A;&#x88AB;&#x4ECE;&#x6E32;&#x67D3;&#x6811;&#x4E2D;&#x79FB;&#x9664;&#xFF0C;&#x7136;&#x540E;Framework&#x4F1A;&#x8C03;&#x7528;<code>element.deactivate</code> &#x65B9;&#x6CD5;&#xFF0C;&#x8FD9;&#x65F6;<code>element</code>&#x72B6;&#x6001;&#x53D8;&#x4E3A;&#x201C;inactive&#x201D;&#x72B6;&#x6001;&#x3002;</li>
<li>&#x201C;inactive&#x201D;&#x6001;&#x7684;element&#x5C06;&#x4E0D;&#x4F1A;&#x518D;&#x663E;&#x793A;&#x5230;&#x5C4F;&#x5E55;&#x3002;&#x4E3A;&#x4E86;&#x907F;&#x514D;&#x5728;&#x4E00;&#x6B21;&#x52A8;&#x753B;&#x6267;&#x884C;&#x8FC7;&#x7A0B;&#x4E2D;&#x53CD;&#x590D;&#x521B;&#x5EFA;&#x3001;&#x79FB;&#x9664;&#x67D0;&#x4E2A;&#x7279;&#x5B9A;element&#xFF0C;&#x201C;inactive&#x201D;&#x6001;&#x7684;element&#x5728;&#x5F53;&#x524D;&#x52A8;&#x753B;&#x6700;&#x540E;&#x4E00;&#x5E27;&#x7ED3;&#x675F;&#x524D;&#x90FD;&#x4F1A;&#x4FDD;&#x7559;&#xFF0C;&#x5982;&#x679C;&#x5728;&#x52A8;&#x753B;&#x6267;&#x884C;&#x7ED3;&#x675F;&#x540E;&#x5B83;&#x8FD8;&#x672A;&#x80FD;&#x91CD;&#x65B0;&#x53D8;&#x6210;&#x201C;active&#x201D;&#x72B6;&#x6001;&#xFF0C;Framework&#x5C31;&#x4F1A;&#x8C03;&#x7528;&#x5176;<code>unmount</code>&#x65B9;&#x6CD5;&#x5C06;&#x5176;&#x5F7B;&#x5E95;&#x79FB;&#x9664;&#xFF0C;&#x8FD9;&#x65F6;element&#x7684;&#x72B6;&#x6001;&#x4E3A;<code>defunct</code>,&#x5B83;&#x5C06;&#x6C38;&#x8FDC;&#x4E0D;&#x4F1A;&#x518D;&#x88AB;&#x63D2;&#x5165;&#x5230;&#x6811;&#x4E2D;&#x3002;</li>
<li>&#x5982;&#x679C;<code>element</code>&#x8981;&#x91CD;&#x65B0;&#x63D2;&#x5165;&#x5230;Element&#x6811;&#x7684;&#x5176;&#x5B83;&#x4F4D;&#x7F6E;&#xFF0C;&#x5982;<code>element</code>&#x6216;<code>element</code>&#x7684;&#x7956;&#x5148;&#x62E5;&#x6709;&#x4E00;&#x4E2A;GlobalKey&#xFF08;&#x7528;&#x4E8E;&#x5168;&#x5C40;&#x590D;&#x7528;&#x5143;&#x7D20;&#xFF09;&#xFF0C;&#x90A3;&#x4E48;Framework&#x4F1A;&#x5148;&#x5C06;element&#x4ECE;&#x73B0;&#x6709;&#x4F4D;&#x7F6E;&#x79FB;&#x9664;&#xFF0C;&#x7136;&#x540E;&#x518D;&#x8C03;&#x7528;&#x5176;<code>activate</code>&#x65B9;&#x6CD5;&#xFF0C;&#x5E76;&#x5C06;&#x5176;<code>renderObject</code>&#x91CD;&#x65B0;attach&#x5230;&#x6E32;&#x67D3;&#x6811;&#x3002;</li>
</ol>
<p>&#x770B;&#x5B8C;Element&#x7684;&#x751F;&#x547D;&#x5468;&#x671F;&#xFF0C;&#x53EF;&#x80FD;&#x6709;&#x4E9B;&#x8BFB;&#x8005;&#x4F1A;&#x6709;&#x7591;&#x95EE;&#xFF0C;&#x5F00;&#x53D1;&#x8005;&#x4F1A;&#x76F4;&#x63A5;&#x64CD;&#x4F5C;Element&#x6811;&#x5417;&#xFF1F;&#x5176;&#x5B9E;&#x5BF9;&#x4E8E;&#x5F00;&#x53D1;&#x8005;&#x6765;&#x8BF4;&#xFF0C;&#x5927;&#x591A;&#x6570;&#x60C5;&#x51B5;&#x4E0B;&#x53EA;&#x9700;&#x8981;&#x5173;&#x6CE8;Widget&#x6811;&#x5C31;&#x884C;&#xFF0C;Flutter&#x6846;&#x67B6;&#x5DF2;&#x7ECF;&#x5C06;&#x5BF9;Widget&#x6811;&#x7684;&#x64CD;&#x4F5C;&#x6620;&#x5C04;&#x5230;&#x4E86;Element&#x6811;&#x4E0A;&#xFF0C;&#x8FD9;&#x53EF;&#x4EE5;&#x6781;&#x5927;&#x7684;&#x964D;&#x4F4E;&#x590D;&#x6742;&#x5EA6;&#xFF0C;&#x63D0;&#x9AD8;&#x5F00;&#x53D1;&#x6548;&#x7387;&#x3002;&#x4F46;&#x662F;&#x4E86;&#x89E3;Element&#x5BF9;&#x7406;&#x89E3;&#x6574;&#x4E2A;Flutter UI&#x6846;&#x67B6;&#x662F;&#x81F3;&#x5173;&#x91CD;&#x8981;&#x7684;&#xFF0C;Flutter&#x6B63;&#x662F;&#x901A;&#x8FC7;Element&#x8FD9;&#x4E2A;&#x7EBD;&#x5E26;&#x5C06;Widget&#x548C;RenderObject&#x5173;&#x8054;&#x8D77;&#x6765;&#xFF0C;&#x4E86;&#x89E3;Element&#x5C42;&#x4E0D;&#x4EC5;&#x4F1A;&#x5E2E;&#x52A9;&#x8BFB;&#x8005;&#x5BF9;Flutter UI&#x6846;&#x67B6;&#x6709;&#x4E2A;&#x6E05;&#x6670;&#x7684;&#x8BA4;&#x8BC6;&#xFF0C;&#x800C;&#x4E14;&#x4E5F;&#x4F1A;&#x63D0;&#x9AD8;&#x81EA;&#x5DF1;&#x7684;&#x62BD;&#x8C61;&#x80FD;&#x529B;&#x548C;&#x8BBE;&#x8BA1;&#x80FD;&#x529B;&#x3002;&#x53E6;&#x5916;&#x5728;&#x6709;&#x4E9B;&#x65F6;&#x5019;&#xFF0C;&#x6211;&#x4EEC;&#x5FC5;&#x987B;&#x5F97;&#x76F4;&#x63A5;&#x4F7F;&#x7528;Element&#x5BF9;&#x8C61;&#x6765;&#x5B8C;&#x6210;&#x4E00;&#x4E9B;&#x64CD;&#x4F5C;&#xFF0C;&#x6BD4;&#x5982;&#x83B7;&#x53D6;&#x4E3B;&#x9898;Theme&#x6570;&#x636E;&#xFF0C;&#x5177;&#x4F53;&#x7EC6;&#x8282;&#x5C06;&#x5728;&#x4E0B;&#x6587;&#x4ECB;&#x7ECD;&#x3002;</p>
<h2 id="1422-buildcontext">14.2.2 BuildContext</h2>
<p>&#x6211;&#x4EEC;&#x5DF2;&#x7ECF;&#x77E5;&#x9053;&#xFF0C;<code>StatelessWidget</code>&#x548C;<code>StatefulWidget</code>&#x7684;<code>build</code>&#x65B9;&#x6CD5;&#x90FD;&#x4F1A;&#x4F20;&#x4E00;&#x4E2A;<code>BuildContext</code>&#x5BF9;&#x8C61;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">Widget <span class="token function">build</span><span class="token punctuation">(</span>BuildContext context<span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
</code></pre>
<p>&#x6211;&#x4EEC;&#x4E5F;&#x77E5;&#x9053;&#xFF0C;&#x5728;&#x5F88;&#x591A;&#x65F6;&#x5019;&#x6211;&#x4EEC;&#x90FD;&#x9700;&#x8981;&#x4F7F;&#x7528;&#x8FD9;&#x4E2A;<code>context</code> &#x505A;&#x4E00;&#x4E9B;&#x4E8B;&#xFF0C;&#x6BD4;&#x5982;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">Theme<span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>context<span class="token punctuation">)</span> <span class="token comment">//&#x83B7;&#x53D6;&#x4E3B;&#x9898;</span>
Navigator<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span>context<span class="token punctuation">,</span> route<span class="token punctuation">)</span> <span class="token comment">//&#x5165;&#x6808;&#x65B0;&#x8DEF;&#x7531;</span>
Localizations<span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span>context<span class="token punctuation">,</span> type<span class="token punctuation">)</span> <span class="token comment">//&#x83B7;&#x53D6;Local</span>
context<span class="token punctuation">.</span>size <span class="token comment">//&#x83B7;&#x53D6;&#x4E0A;&#x4E0B;&#x6587;&#x5927;&#x5C0F;</span>
context<span class="token punctuation">.</span><span class="token function">findRenderObject</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">//&#x67E5;&#x627E;&#x5F53;&#x524D;&#x6216;&#x6700;&#x8FD1;&#x7684;&#x4E00;&#x4E2A;&#x7956;&#x5148;RenderObject</span>
</code></pre>
<p>&#x90A3;&#x4E48;<code>BuildContext</code>&#x5230;&#x5E95;&#x662F;&#x4EC0;&#x4E48;&#x5462;&#xFF0C;&#x67E5;&#x770B;&#x5176;&#x5B9A;&#x4E49;&#xFF0C;&#x53D1;&#x73B0;&#x5176;&#x662F;&#x4E00;&#x4E2A;&#x62BD;&#x8C61;&#x63A5;&#x53E3;&#x7C7B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">abstract</span> <span class="token keyword">class</span> <span class="token class-name">BuildContext</span> <span class="token punctuation">{</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x90A3;&#x8FD9;&#x4E2A;<code>context</code>&#x5BF9;&#x8C61;&#x5BF9;&#x5E94;&#x7684;&#x5B9E;&#x73B0;&#x7C7B;&#x5230;&#x5E95;&#x662F;&#x8C01;&#x5462;&#xFF1F;&#x6211;&#x4EEC;&#x987A;&#x85E4;&#x6478;&#x74DC;&#xFF0C;&#x53D1;&#x73B0;<code>build</code>&#x8C03;&#x7528;&#x662F;&#x53D1;&#x751F;&#x5728;<code>StatelessWidget</code>&#x548C;<code>StatefulWidget</code>&#x5BF9;&#x5E94;&#x7684;<code>StatelessElement</code>&#x548C;<code>StatefulElement</code>&#x7684;<code>build</code>&#x65B9;&#x6CD5;&#x4E2D;&#xFF0C;&#x4EE5;<code>StatelessElement</code>&#x4E3A;&#x4F8B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart">
<span class="token keyword">class</span> <span class="token class-name">StatelessElement</span> <span class="token keyword">extends</span> <span class="token class-name">ComponentElement</span> <span class="token punctuation">{</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
  <span class="token metadata symbol">@override</span>
  Widget <span class="token function">build</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">&gt;</span> widget<span class="token punctuation">.</span><span class="token function">build</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x53D1;&#x73B0;<code>build</code>&#x4F20;&#x9012;&#x7684;&#x53C2;&#x6570;&#x662F;<code>this</code>&#xFF0C;&#x5F88;&#x660E;&#x663E;&#xFF01;&#x8FD9;&#x4E2A;<code>BuildContext</code>&#x5C31;&#x662F;<code>StatelessElement</code>&#x3002;&#x540C;&#x6837;&#xFF0C;&#x6211;&#x4EEC;&#x540C;&#x6837;&#x53D1;&#x73B0;<code>StatefulWidget</code>&#x7684;<code>context</code>&#x662F;<code>StatefulElement</code>&#x3002;&#x4F46;<code>StatelessElement</code>&#x548C;<code>StatefulElement</code>&#x672C;&#x8EAB;&#x5E76;&#x6CA1;&#x6709;&#x5B9E;&#x73B0;<code>BuildContext</code>&#x63A5;&#x53E3;&#xFF0C;&#x7EE7;&#x7EED;&#x8DDF;&#x8E2A;&#x4EE3;&#x7801;&#xFF0C;&#x53D1;&#x73B0;&#x5B83;&#x4EEC;&#x95F4;&#x63A5;&#x7EE7;&#x627F;&#x81EA;<code>Element</code>&#x7C7B;&#xFF0C;&#x7136;&#x540E;&#x67E5;&#x770B;<code>Element</code>&#x7C7B;&#x5B9A;&#x4E49;&#xFF0C;&#x53D1;&#x73B0;<code>Element</code>&#x7C7B;&#x679C;&#x7136;&#x5B9E;&#x73B0;&#x4E86;<code>BuildContext</code>&#x63A5;&#x53E3;:</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">class</span> <span class="token class-name">Element</span> <span class="token keyword">extends</span> <span class="token class-name">DiagnosticableTree</span> <span class="token keyword">implements</span> <span class="token class-name">BuildContext</span> <span class="token punctuation">{</span>
    <span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x81F3;&#x6B64;&#x771F;&#x76F8;&#x5927;&#x767D;&#xFF0C;<code>BuildContext</code>&#x5C31;&#x662F;widget&#x5BF9;&#x5E94;&#x7684;<code>Element</code>&#xFF0C;&#x6240;&#x4EE5;&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x901A;&#x8FC7;<code>context</code>&#x5728;<code>StatelessWidget</code>&#x548C;<code>StatefulWidget</code>&#x7684;<code>build</code>&#x65B9;&#x6CD5;&#x4E2D;&#x76F4;&#x63A5;&#x8BBF;&#x95EE;<code>Element</code>&#x5BF9;&#x8C61;&#x3002;&#x6211;&#x4EEC;&#x83B7;&#x53D6;&#x4E3B;&#x9898;&#x6570;&#x636E;&#x7684;&#x4EE3;&#x7801;<code>Theme.of(context)</code>&#x5185;&#x90E8;&#x6B63;&#x662F;&#x8C03;&#x7528;&#x4E86;Element&#x7684;<code>inheritFromWidgetOfExactType()</code>&#x65B9;&#x6CD5;&#x3002;</p>
<blockquote>
<p>&#x601D;&#x8003;&#x9898;&#xFF1A;&#x4E3A;&#x4EC0;&#x4E48;build&#x65B9;&#x6CD5;&#x7684;&#x53C2;&#x6570;&#x4E0D;&#x5B9A;&#x4E49;&#x6210;Element&#x5BF9;&#x8C61;&#xFF0C;&#x800C;&#x8981;&#x5B9A;&#x4E49;&#x6210;BuildContext ?</p>
</blockquote>
<h3 id="&#x8FDB;&#x9636;">&#x8FDB;&#x9636;</h3>
<p>&#x6211;&#x4EEC;&#x53EF;&#x4EE5;&#x770B;&#x5230;Element&#x662F;Flutter UI&#x6846;&#x67B6;&#x5185;&#x90E8;&#x8FDE;&#x63A5;widget&#x548C;<code>RenderObject</code>&#x7684;&#x7EBD;&#x5E26;&#xFF0C;&#x5927;&#x591A;&#x6570;&#x65F6;&#x5019;&#x5F00;&#x53D1;&#x8005;&#x53EA;&#x9700;&#x8981;&#x5173;&#x6CE8;widget&#x5C42;&#x5373;&#x53EF;&#xFF0C;&#x4F46;&#x662F;widget&#x5C42;&#x6709;&#x65F6;&#x5019;&#x5E76;&#x4E0D;&#x80FD;&#x5B8C;&#x5168;&#x5C4F;&#x853D;<code>Element</code>&#x7EC6;&#x8282;&#xFF0C;&#x6240;&#x4EE5;Framework&#x5728;<code>StatelessWidget</code>&#x548C;<code>StatefulWidget</code>&#x4E2D;&#x901A;&#x8FC7;<code>build</code>&#x65B9;&#x6CD5;&#x53C2;&#x6570;&#x53C8;&#x5C06;<code>Element</code>&#x5BF9;&#x8C61;&#x4E5F;&#x4F20;&#x9012;&#x7ED9;&#x4E86;&#x5F00;&#x53D1;&#x8005;&#xFF0C;&#x8FD9;&#x6837;&#x4E00;&#x6765;&#xFF0C;&#x5F00;&#x53D1;&#x8005;&#x4FBF;&#x53EF;&#x4EE5;&#x5728;&#x9700;&#x8981;&#x65F6;&#x76F4;&#x63A5;&#x64CD;&#x4F5C;<code>Element</code>&#x5BF9;&#x8C61;&#x3002;&#x90A3;&#x4E48;&#x73B0;&#x5728;&#x7B14;&#x8005;&#x63D0;&#x4E24;&#x4E2A;&#x95EE;&#x9898;&#xFF0C;&#x8BF7;&#x8BFB;&#x8005;&#x5148;&#x81EA;&#x5DF1;&#x601D;&#x8003;&#x4E00;&#x4E0B;&#xFF1A;</p>
<ol>
<li>&#x5982;&#x679C;&#x6CA1;&#x6709;widget&#x5C42;&#xFF0C;&#x5355;&#x9760;<code>Element</code>&#x5C42;&#x662F;&#x5426;&#x53EF;&#x4EE5;&#x642D;&#x5EFA;&#x8D77;&#x4E00;&#x4E2A;&#x53EF;&#x7528;&#x7684;UI&#x6846;&#x67B6;&#xFF1F;&#x5982;&#x679C;&#x53EF;&#x4EE5;&#x5E94;&#x8BE5;&#x662F;&#x4EC0;&#x4E48;&#x6837;&#x5B50;&#xFF1F;</li>
<li>Flutter UI&#x6846;&#x67B6;&#x80FD;&#x4E0D;&#x505A;&#x6210;&#x54CD;&#x5E94;&#x5F0F;&#x5417;&#xFF1F;</li>
</ol>
<p>&#x5BF9;&#x4E8E;&#x95EE;&#x9898;1&#xFF0C;&#x7B54;&#x6848;&#x5F53;&#x7136;&#x662F;&#x80AF;&#x5B9A;&#x7684;&#xFF0C;&#x56E0;&#x4E3A;&#x6211;&#x4EEC;&#x4E4B;&#x524D;&#x8BF4;&#x8FC7;widget&#x6811;&#x53EA;&#x662F;<code>Element</code>&#x6811;&#x7684;&#x6620;&#x5C04;&#xFF0C;&#x6211;&#x4EEC;&#x5B8C;&#x5168;&#x53EF;&#x4EE5;&#x76F4;&#x63A5;&#x901A;&#x8FC7;Element&#x6765;&#x642D;&#x5EFA;&#x4E00;&#x4E2A;UI&#x6846;&#x67B6;&#x3002;&#x4E0B;&#x9762;&#x4E3E;&#x4E00;&#x4E2A;&#x4F8B;&#x5B50;&#xFF1A;</p>
<p>&#x6211;&#x4EEC;&#x901A;&#x8FC7;&#x7EAF;&#x7CB9;&#x7684;Element&#x6765;&#x6A21;&#x62DF;&#x4E00;&#x4E2A;<code>StatefulWidget</code>&#x7684;&#x529F;&#x80FD;&#xFF0C;&#x5047;&#x8BBE;&#x6709;&#x4E00;&#x4E2A;&#x9875;&#x9762;&#xFF0C;&#x8BE5;&#x9875;&#x9762;&#x6709;&#x4E00;&#x4E2A;&#x6309;&#x94AE;&#xFF0C;&#x6309;&#x94AE;&#x7684;&#x6587;&#x672C;&#x662F;&#x4E00;&#x4E2A;9&#x4F4D;&#x6570;&#xFF0C;&#x70B9;&#x51FB;&#x4E00;&#x6B21;&#x6309;&#x94AE;&#xFF0C;&#x5219;&#x5BF9;9&#x4E2A;&#x6570;&#x968F;&#x673A;&#x6392;&#x4E00;&#x6B21;&#x5E8F;&#xFF0C;&#x4EE3;&#x7801;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">class</span> <span class="token class-name">HomeView</span> <span class="token keyword">extends</span> <span class="token class-name">ComponentElement</span><span class="token punctuation">{</span>
  <span class="token function">HomeView</span><span class="token punctuation">(</span>Widget widget<span class="token punctuation">)</span> <span class="token punctuation">:</span> <span class="token keyword">super</span><span class="token punctuation">(</span>widget<span class="token punctuation">)</span><span class="token punctuation">;</span>
  String text <span class="token operator">=</span> <span class="token string">&quot;123456789&quot;</span><span class="token punctuation">;</span>

  <span class="token metadata symbol">@override</span>
  Widget <span class="token function">build</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    Color primary<span class="token operator">=</span>Theme<span class="token punctuation">.</span><span class="token function">of</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">.</span>primaryColor<span class="token punctuation">;</span> <span class="token comment">//1</span>
    <span class="token keyword">return</span> <span class="token function">GestureDetector</span><span class="token punctuation">(</span>
      child<span class="token punctuation">:</span> <span class="token function">Center</span><span class="token punctuation">(</span>
        child<span class="token punctuation">:</span> <span class="token function">FlatButton</span><span class="token punctuation">(</span>
          child<span class="token punctuation">:</span> <span class="token function">Text</span><span class="token punctuation">(</span>text<span class="token punctuation">,</span> style<span class="token punctuation">:</span> <span class="token function">TextStyle</span><span class="token punctuation">(</span>color<span class="token punctuation">:</span> primary<span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
          onPressed<span class="token punctuation">:</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">var</span> t <span class="token operator">=</span> text<span class="token punctuation">.</span><span class="token function">split</span><span class="token punctuation">(</span><span class="token string">&quot;&quot;</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token function">shuffle</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            text <span class="token operator">=</span> t<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token function">markNeedsBuild</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//&#x70B9;&#x51FB;&#x540E;&#x5C06;&#x8BE5;Element&#x6807;&#x8BB0;&#x4E3A;dirty&#xFF0C;Element&#x5C06;&#x4F1A;rebuild</span>
          <span class="token punctuation">}</span><span class="token punctuation">,</span>
        <span class="token punctuation">)</span><span class="token punctuation">,</span>
      <span class="token punctuation">)</span><span class="token punctuation">,</span>
    <span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<ul>
<li>&#x4E0A;&#x9762;<code>build</code>&#x65B9;&#x6CD5;&#x4E0D;&#x63A5;&#x6536;&#x53C2;&#x6570;&#xFF0C;&#x8FD9;&#x4E00;&#x70B9;&#x548C;&#x5728;<code>StatelessWidget</code>&#x548C;<code>StatefulWidget</code>&#x4E2D;<code>build(BuildContext)</code>&#x65B9;&#x6CD5;&#x4E0D;&#x540C;&#x3002;&#x4EE3;&#x7801;&#x4E2D;&#x9700;&#x8981;&#x7528;&#x5230;<code>BuildContext</code>&#x7684;&#x5730;&#x65B9;&#x76F4;&#x63A5;&#x7528;<code>this</code>&#x4EE3;&#x66FF;&#x5373;&#x53EF;&#xFF0C;&#x5982;&#x4EE3;&#x7801;&#x6CE8;&#x91CA;1&#x5904;<code>Theme.of(this)</code>&#x53C2;&#x6570;&#x76F4;&#x63A5;&#x4F20;<code>this</code>&#x5373;&#x53EF;&#xFF0C;&#x56E0;&#x4E3A;&#x5F53;&#x524D;&#x5BF9;&#x8C61;&#x672C;&#x8EAB;&#x5C31;&#x662F;<code>Element</code>&#x5B9E;&#x4F8B;&#x3002;</li>
<li><p>&#x5F53;<code>text</code>&#x53D1;&#x751F;&#x6539;&#x53D8;&#x65F6;&#xFF0C;&#x6211;&#x4EEC;&#x8C03;&#x7528;<code>markNeedsBuild()</code>&#x65B9;&#x6CD5;&#x5C06;&#x5F53;&#x524D;Element&#x6807;&#x8BB0;&#x4E3A;dirty&#x5373;&#x53EF;&#xFF0C;&#x6807;&#x8BB0;&#x4E3A;dirty&#x7684;Element&#x4F1A;&#x5728;&#x4E0B;&#x4E00;&#x5E27;&#x4E2D;&#x91CD;&#x5EFA;&#x3002;&#x5B9E;&#x9645;&#x4E0A;&#xFF0C;<code>State.setState()</code>&#x5728;&#x5185;&#x90E8;&#x4E5F;&#x662F;&#x8C03;&#x7528;&#x7684;<code>markNeedsBuild()</code>&#x65B9;&#x6CD5;&#x3002;</p>
</li>
<li><p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;build&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x4ECD;&#x7136;&#x662F;&#x4E00;&#x4E2A;widget&#xFF0C;&#x8FD9;&#x662F;&#x7531;&#x4E8E;Flutter&#x6846;&#x67B6;&#x4E2D;&#x5DF2;&#x7ECF;&#x6709;&#x4E86;widget&#x8FD9;&#x4E00;&#x5C42;&#xFF0C;&#x5E76;&#x4E14;&#x7EC4;&#x4EF6;&#x5E93;&#x90FD;&#x5DF2;&#x7ECF;&#x662F;&#x4EE5;widget&#x7684;&#x5F62;&#x5F0F;&#x63D0;&#x4F9B;&#x4E86;&#xFF0C;&#x5982;&#x679C;&#x5728;Flutter&#x6846;&#x67B6;&#x4E2D;&#x6240;&#x6709;&#x7EC4;&#x4EF6;&#x90FD;&#x50CF;&#x793A;&#x4F8B;&#x7684;<code>HomeView</code>&#x4E00;&#x6837;&#x4EE5;<code>Element</code>&#x5F62;&#x5F0F;&#x63D0;&#x4F9B;&#xFF0C;&#x90A3;&#x4E48;&#x5C31;&#x53EF;&#x4EE5;&#x7528;&#x7EAF;<code>Element</code>&#x6765;&#x6784;&#x5EFA;UI&#x4E86;<code>HomeView</code>&#x7684;build&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x503C;&#x7C7B;&#x578B;&#x5C31;&#x53EF;&#x4EE5;&#x662F;<code>Element</code>&#x4E86;&#x3002;</p>
</li>
</ul>
<p>&#x5982;&#x679C;&#x6211;&#x4EEC;&#x9700;&#x8981;&#x5C06;&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x5728;&#x73B0;&#x6709;Flutter&#x6846;&#x67B6;&#x4E2D;&#x8DD1;&#x8D77;&#x6765;&#xFF0C;&#x90A3;&#x4E48;&#x8FD8;&#x662F;&#x5F97;&#x63D0;&#x4F9B;&#x4E00;&#x4E2A;&#x201C;&#x9002;&#x914D;&#x5668;&#x201D;widget&#x5C06;<code>HomeView</code>&#x7ED3;&#x5408;&#x5230;&#x73B0;&#x6709;&#x6846;&#x67B6;&#x4E2D;&#xFF0C;&#x4E0B;&#x9762;<code>CustomHome</code>&#x5C31;&#x76F8;&#x5F53;&#x4E8E;&#x201C;&#x9002;&#x914D;&#x5668;&#x201D;&#xFF1A;</p>
<pre class="language-"><code class="lang-dart"><span class="token keyword">class</span> <span class="token class-name">CustomHome</span> <span class="token keyword">extends</span> <span class="token class-name">Widget</span> <span class="token punctuation">{</span>
  <span class="token metadata symbol">@override</span>
  Element <span class="token function">createElement</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token function">HomeView</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>&#x73B0;&#x5728;&#x5C31;&#x53EF;&#x4EE5;&#x5C06;<code>CustomHome</code>&#x6DFB;&#x52A0;&#x5230;widget&#x6811;&#x4E86;&#xFF0C;&#x6211;&#x4EEC;&#x5728;&#x4E00;&#x4E2A;&#x65B0;&#x8DEF;&#x7531;&#x9875;&#x521B;&#x5EFA;&#x5B83;&#xFF0C;&#x6700;&#x7EC8;&#x6548;&#x679C;&#x5982;&#x4E0B;&#x5982;&#x56FE;14-1&#x548C;14-2&#xFF08;&#x70B9;&#x51FB;&#x540E;&#xFF09;&#x6240;&#x793A;&#xFF1A;</p>
<p><img src="https://pcdn.flutterchina.club/imgs/14-1.png" alt="&#x56FE;14-1"> <img src="https://pcdn.flutterchina.club/imgs/14-2.png" alt="&#x56FE;14-2"></p>
<p>&#x70B9;&#x51FB;&#x6309;&#x94AE;&#x5219;&#x6309;&#x94AE;&#x6587;&#x672C;&#x4F1A;&#x968F;&#x673A;&#x6392;&#x5E8F;&#x3002;</p>
<p>&#x5BF9;&#x4E8E;&#x95EE;&#x9898;2&#xFF0C;&#x7B54;&#x6848;&#x5F53;&#x7136;&#x4E5F;&#x662F;&#x80AF;&#x5B9A;&#x7684;&#xFF0C;Flutter engine&#x63D0;&#x4F9B;&#x7684;dart API&#x662F;&#x539F;&#x59CB;&#x4E14;&#x72EC;&#x7ACB;&#x7684;&#xFF0C;&#x8FD9;&#x4E2A;&#x4E0E;&#x64CD;&#x4F5C;&#x7CFB;&#x7EDF;&#x63D0;&#x4F9B;&#x7684;API&#x7C7B;&#x4F3C;&#xFF0C;&#x4E0A;&#x5C42;UI&#x6846;&#x67B6;&#x8BBE;&#x8BA1;&#x6210;&#x4EC0;&#x4E48;&#x6837;&#x5B8C;&#x5168;&#x53D6;&#x51B3;&#x4E8E;&#x8BBE;&#x8BA1;&#x8005;&#xFF0C;&#x5B8C;&#x5168;&#x53EF;&#x4EE5;&#x5C06;UI&#x6846;&#x67B6;&#x8BBE;&#x8BA1;&#x6210;Android&#x98CE;&#x683C;&#x6216;iOS&#x98CE;&#x683C;&#xFF0C;&#x4F46;&#x8FD9;&#x4E9B;&#x4E8B;Google&#x4E0D;&#x4F1A;&#x518D;&#x53BB;&#x505A;&#xFF0C;&#x6211;&#x4EEC;&#x4E5F;&#x6CA1;&#x5FC5;&#x8981;&#x518D;&#x53BB;&#x641E;&#x8FD9;&#x4E00;&#x5957;&#xFF0C;&#x8FD9;&#x662F;&#x56E0;&#x4E3A;&#x54CD;&#x5E94;&#x5F0F;&#x7684;&#x601D;&#x60F3;&#x672C;&#x8EAB;&#x662F;&#x5F88;&#x68D2;&#x7684;&#xFF0C;&#x4E4B;&#x6240;&#x4EE5;&#x63D0;&#x51FA;&#x8FD9;&#x4E2A;&#x95EE;&#x9898;&#xFF0C;&#x662F;&#x56E0;&#x4E3A;&#x7B14;&#x8005;&#x8BA4;&#x4E3A;&#x505A;&#x4E0E;&#x4E0D;&#x505A;&#x662F;&#x4E00;&#x56DE;&#x4E8B;&#xFF0C;&#x4F46;&#x77E5;&#x9053;&#x80FD;&#x4E0D;&#x80FD;&#x505A;&#x662F;&#x53E6;&#x4E00;&#x56DE;&#x4E8B;&#xFF0C;&#x8FD9;&#x80FD;&#x53CD;&#x6620;&#x51FA;&#x6211;&#x4EEC;&#x5BF9;&#x77E5;&#x8BC6;&#x7684;&#x7406;&#x89E3;&#x7A0B;&#x5EA6;&#x3002;</p>
<h3 id="&#x603B;&#x7ED3;">&#x603B;&#x7ED3;</h3>
<p>&#x672C;&#x8282;&#x8BE6;&#x7EC6;&#x7684;&#x4ECB;&#x7ECD;&#x4E86;<code>Element</code>&#x7684;&#x751F;&#x547D;&#x5468;&#x671F;&#xFF0C;&#x4EE5;&#x53CA;&#x5B83;Widget&#x3001;BuildContext&#x7684;&#x5173;&#x7CFB;&#xFF0C;&#x4E5F;&#x4ECB;&#x7ECD;&#x4E86;Element&#x5728;Flutter UI&#x7CFB;&#x7EDF;&#x4E2D;&#x7684;&#x89D2;&#x8272;&#x548C;&#x4F5C;&#x7528;&#xFF0C;&#x6211;&#x4EEC;&#x5C06;&#x5728;&#x4E0B;&#x4E00;&#x8282;&#x4ECB;&#x7ECD;Flutter UI&#x7CFB;&#x7EDF;&#x4E2D;&#x53E6;&#x4E00;&#x4E2A;&#x91CD;&#x8981;&#x7684;&#x89D2;&#x8272;RenderObject&#x3002;</p>

                                
                                </section>
                            
    </div>
    <div class="search-results">
        <div class="has-results">
            
            <h1 class="search-results-title"><span class='search-results-count'></span> results matching "<span class='search-query'></span>"</h1>
            <ul class="search-results-list"></ul>
            
        </div>
        <div class="no-results">
            
            <h1 class="search-results-title">No results matching "<span class='search-query'></span>"</h1>
            
        </div>
    </div>
</div>

                        </div>
                    </div>
                
            </div>

            
                
                <a href="flutter_ui_system.html" class="navigation navigation-prev " aria-label="Previous page: 14.1：Flutter UI系统">
                    <i class="fa fa-angle-left"></i>
                </a>
                
                
                <a href="render_object.html" class="navigation navigation-next " aria-label="Next page: 14.3：RenderObject与RenderBox">
                    <i class="fa fa-angle-right"></i>
                </a>
                
            
        
    </div>

    <script>
        var gitbook = gitbook || [];
        gitbook.push(function() {
            gitbook.page.hasChanged({"page":{"title":"14.2：Element和BuildContext","level":"3.7.2","depth":2,"next":{"title":"14.3：RenderObject与RenderBox","level":"3.7.3","depth":2,"path":"chapter14/render_object.md","ref":"chapter14/render_object.md","articles":[]},"previous":{"title":"14.1：Flutter UI系统","level":"3.7.1","depth":2,"path":"chapter14/flutter_ui_system.md","ref":"chapter14/flutter_ui_system.md","articles":[]},"dir":"ltr"},"config":{"plugins":["-search","search-pro","ace","splitter","prism","donate","-highlight"],"root":"docs","styles":{"website":"styles/website.css","ebook":"styles/ebook.css","pdf":"styles/pdf.css","mobi":"styles/mobi.css","epub":"styles/epub.css"},"pluginsConfig":{"prism":{"lang":{"shell":"bash"}},"ace":{},"splitter":{},"search-pro":{"cutWordLib":"nodejieba","defineWord":["Gitbook Use"]},"lunr":{"maxIndexSize":1000000,"ignoreSpecialCharacters":false},"donate":{"alipay":"","alipayText":"支付宝打赏","button":"赏","title":"","wechat":"https://cdn.jsdelivr.net/gh/flutterchina/flutter-in-action@1.0.3/docs/imgs/pay.jpeg","wechatText":"微信打赏"},"fontsettings":{"theme":"white","family":"sans","size":2},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"theme-default":{"styles":{"website":"styles/website.css","pdf":"styles/pdf.css","epub":"styles/epub.css","mobi":"styles/mobi.css","ebook":"styles/ebook.css","print":"styles/print.css"},"showLevel":false}},"theme":"default","author":"wendux 824783146@qq.com","bookRoot":"https://book.flutterchina.club/","pdf":{"pageNumbers":true,"fontSize":12,"fontFamily":"Arial","paperSize":"a4","chapterMark":"pagebreak","pageBreaksBefore":"/","margin":{"right":62,"left":62,"top":56,"bottom":56}},"structure":{"langs":"LANGS.md","readme":"README.md","glossary":"GLOSSARY.md","summary":"SUMMARY.md"},"variables":{},"title":"《Flutter实战》","language":"zh-hans","links":{"sharing":{"all":null,"facebook":null,"google":null,"twitter":null,"weibo":null},"sidebar":{"<div><img height=20 style='position:relative; top:5px; padding-right:5px ' src='https://cdn.jsdelivr.net/gh/flutterchina/website@1.0/images/favicon.png'/> Flutter中文网</div>":"https://flutterchina.club"}},"gitbook":"*","description":"记录Gitbook的配置和一些插件的使用"},"file":{"path":"chapter14/element_buildcontext.md","mtime":"2019-08-22T07:10:57.398Z","type":"markdown"},"gitbook":{"version":"3.2.3","time":"2020-03-15T14:52:22.710Z"},"basePath":"..","book":{"language":""}});
        });
    </script>
</div>



    <script src="https://pcdn.flutterchina.club/gitbook/gitbook.js"></script>
    <script src="https://pcdn.flutterchina.club/gitbook/theme.js"></script>
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-search-pro/jquery.mark.min.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-search-pro/search.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-ace/ace/ace.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-ace/ace.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-splitter/splitter.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-donate/plugin.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-lunr/lunr.min.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-lunr/search-lunr.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-sharing/buttons.js"></script>
        
    
        
        <script src="https://pcdn.flutterchina.club/gitbook/gitbook-plugin-fontsettings/fontsettings.js"></script>
        
    


<script src="https://pcdn.flutterchina.club/gitbook/pub.js"></script>
<script>
    hookAjax({
        open: function (arg, xhr) {
            if (location.hostname !== 'localhost') {
                if (arg[1][0] === '.') arg[1] = arg[1].slice(1);
                arg[1] = "https://pcdn.flutterchina.club" + arg[1].replace(".html", ".1")
            }
        },
        setRequestHeader: function (arg, xhr) {
            console.log(arg[0], arg[1]);
            if (arg[0] !== 'Accept') return true;
        },
        onload:function(){
            setTimeout(addAD);
        }
    })
</script>
</body>

</html>

